In a wireless network, a wireless communication device (e.g., a Mobile Station (MS) or User Equipment (UE)) communicates with one or more network nodes which provide radio access to send and/or receive information, such as voice traffic, data traffic, and control signals. In particular, control plane signaling and/or user plane data to and from the wireless communication device are carried over a communication layer. Examples of communication layers include a cellular layer and a device-to-device (D2D) layer. In the cellular layer, signals are communicated between the wireless communication device and a network node, such as a base station or eNodeB. In the D2D layer, signals are communicated directly between a first D2D wireless communication device and a second D2D wireless communication device. Such communication can be either assisted by the cellular network infrastructure when it is available, or it can happen in an autonomous fashion in case the cellular network is damaged. The use of D2D communications for proximity services (ProSe) in the cellular spectrum increases the spectrum utilization because a pair of UEs communicating in D2D mode may reuse the cellular spectrum resources such as the uplink and/or downlink physical resource blocks (PRB) of a 3GPP LTE system. With respect to both the cellular layer and the D2D layer, network nodes are responsible for assigning resources. Assignment of resources may be based on radio conditions on the network.
Resource preemption is a well-known technique for managing radio bearer (RB) resources or other radio resources in a wireless network. In preemption, resources are de-allocated from a lower priority communication session (the preempted communication session) and reallocated to a higher priority communication session. In 3GPP Long Term Evolution (LTE) networks, for example, each RB is associated with a so called Allocation and Retention Priority (ARP) level. If the network is congested, the ARP level allows the base station (eNodeB or eNB) to decide whether or not a new request for a radio bearer has a high enough priority to preempt an ongoing bearer and, if yes, which ongoing bearer(s) should be preempted in order to free up resources, e.g., which ongoing bearer(s) have a lower priority.
In 3GPP LTE networks, the eNB is responsible for ensuring that the necessary quality of service (QoS) for a bearer over the radio interface is maintained. In LTE, each bearer is associated with an allocation and retention priority (ARP) indicator that is used by the eNB in congestion situations to decide which bearer can be dropped (preempted) or must be maintained (retained). ARP is also used to make admission decisions of newly arriving RB requests. For example, an arriving high priority RB request can be granted by the eNB even in a congestion situation by preempting an ongoing low priority RB. A low priority RB can also be preempted in order to maintain the QoS of ongoing high ARP bearers.
For example, in legacy 3GPP LTE networks, ARP settings along with other QoS attributes are transferred by the core network to the eNB at radio bearer setup request. Also, the ARP contains information about the priority level, the pre-emption capability indicator (PCI) and the pre-emption vulnerability indicator (PVI) related to the bearer request. The PCI information defines whether a certain bearer can tear down (preempt) some other bearers in the system with lower ARP priority in order to free up resources for the new preemption-capable bearer. The PVI defines whether a bearer is vulnerable to be torn down (should not be preempted) by a preemption-capable bearer.
ARP is also used by radio admission control (RAC) procedures that are intertwined with preemption and retention decisions. RAC typically discriminates bearers on the basis of ARP values to decide whether a given bearer can be admitted or not. Such decision is particularly critical especially in high load scenarios, since on one hand high priority ARP bearers should not be penalized too much, but on the other hand the service integrity of already existing guaranteed bit rate (GBR) bearers should be preserved. In this perspective, RAC protects the cell from congestion risks that may compromise service integrity and retain-ability of the served high-priority bearers, e.g., GBR bearers, especially in highly loaded scenario. At the same time, RAC ensures a certain degree of accessibility to radio resources for services that have high priority (e.g., emergency calls) or privileged access (e.g., business subscriptions).
In order to meet this goal, legacy systems employ/trigger ARP prioritization by monitoring different resources also called Monitored System Resources (MSR). MSR may include radio resources (e.g., PRB utilization, physical downlink/uplink control channel resources), computational resources (e.g., eNB baseband capacity utilization, scheduling entities or transmission time interval utilization) or bearer configuration related resources (e.g., maximum number of radio resource control (RRC) Connected UEs per cell (eNB), max numbers of active bearers per cell).
In existing cellular networks supporting D2D communications, a problem arises of how to prioritize among new cellular bearer requests, new D2D bearer requests, ongoing cellular bearers, and ongoing D2D bearers. In other words, a technical problem—specific to networks supporting D2D bearers—is how to enable the eNB to make retention and preemption decisions in case of congestion at the cellular layer and/or D2D layer. In a broader sense, a problem is how to manage (avoid or mitigate) congestion in integrated cellular-D2D networks. This problem is important in cellular-D2D networks, which support both commercial and mission critical (public safety) cellular and proximity services.
Existing radio resource management techniques concerned with radio resource allocation, power control, mode selection and scheduling typically focus on minimizing the impact of D2D communication on the cellular traffic, increasing the overall spectral and energy efficiency and handling seamless mobility between the cellular and D2D layers. Existing D2D radio resource management techniques assume that the D2D layer carries lower priority traffic and the cellular layer must be protected from interference caused by the D2D layer. Existing solutions, however, lack mechanisms that allow the eNB to manage congestion situations in integrated cellular-D2D networks. In known solutions for such networks, the D2D layer is given lower priority than the cellular layer and congestion primarily affects the D2D traffic, irrespectively of the importance of the ongoing or newly arriving cellular or D2D bearers.
Thus, a problem of existing technical solutions is that the radio access network lacks mechanisms to decide which cellular and D2D bearers should be retained/pre-empted in a congestion situation.